A Comparison between Initial and Effective Fundamental Period of RC Frames with Steel Eccentric Bracing

In earthquake resistant designs the value of fundamental period needs to be set close to reality. Special emphasis can be placed on designs which are based either on static equivalent method or performance level. The static equivalent method employs the seismic factor which is strongly dependant on fundamental period. Also during the later design, target displacement is directly connected with square of fundamental period. In this connection most of seismic codes (including Iranian National Seismic Standard) offer an experimental equation distributed for different structural systems to present fundamental period. To make sure for required modifications on seismic design codes, one hundred eighty concrete moment resisting frames with steel eccentric braces has been considered to capture vibration period by performing two-dimensional nonlinear pushover analyses. Pushover Analyses have been conducted using SAP-2000 program, which can consider material nonlinearities almost near reality. In this case the applied forces have been considered as the lateral forces of the Seismic Standard. At the end, fundamental period and effective fundamental period both derived by analysis and the experimental has been discussed concerning bracing kind of spans, length of link beam and height of structure. Analytical results confirm the validity of the experimental equation for presenting fundamental period in the case of reminded frames. (Mohammad Reza Hoseinzadeh, Ali Edalatbehbahani, Mojtaba Labibzadeh. A Comparison between Initial and Effective Fundamental Period of RC Frames with Steel Eccentric Bracing. Journal of American Science 2011; 7(7):876-881). (ISSN: 1545-1003). http://www.americanscience.org